Within recent years, telephone sets incorporating push-button arrays, commonly including twelve such push-buttons, have come into widespread use and have largely supplanted the previously common rotary dial-type telephone. The individual push-buttons comprising such a telephone set array normally project through the cover of the telephone, or a portion of the telephone cover. The remainder of the switching array is contained beneath this outer shell of the telephone set. Such telephone sets are also employed in coin-operated pay stations which are generally located in high volume traffic areas where they are subject to damage from environmental hazards, including especially dust, sugar containing liquids, and the like which can readily seep through the openings surrounding the individual push-button keys and cause damage, in some cases irreparable damage, to the underlying switching device. In such installations, there is also a great likelihood of damage resulting from vandalism, and a protected push-button switch which is permanently attached, and not easily removed, and yet allowing effective operation of the telephone is very desirable.
Several types of covering elements have been previously proposed for use in connection with push-button type telephones, but these have not fully addressed the foregoing problems of providing a protected push-button array to prevent damage. For example, patents such as U.S. Pat. Nos. 3,739,105; 3,927,282; 4,002,855; and 3,345,769, have been concerned with a variety of problems including arrangement for facilitating actuation of the buttons by varying spacing of the actuating means for the individual push-buttons, or in the case of the U.S. Pat. No. 3,345,769 patent, providing a means for supporting message pads or the like.
In certain of my aforementioned patents and applications, a protective covering device is disclosed which provides a flexible sheet or membrane that overlies the pushbuttons. In front of each key this membrane is formed with a thickened region or projection that itself normally bears indicia identifying the particular key. The membrane is continuous, so that it completely seals in the delicate underlying switches.
Such an arrangement has not, however, proven highly vandal resistant. The elastomeric sheet is normally adhesively bonded to the front face of the support plate so that it can be peeled off simply by starting at a corner and working across. This exposes the delicate underlying push-button mechanism, and makes the phone a likely candidate for vandalizing and destruction by the elements.
Another problem with this known arrangement is that the buttons can wear and become illegible. They are mainly made of the same relatively soft material as the seal membrane, so that normal use alone is capable of wearing them down.
The above problems are solved with the invention deseribed in my application Ser. No. 544,391 U.S. Pat. No. 4,555,600, where a standard keypad was used that comprises a rigid support plate having a front face and formed with an array of throughgoing apertures with respective telephone push-buttons projecting at the apertures through the plate past the front face thereof.
In accordance with that invention, an assembly was provided which includes a continuous flexible membrane which overlies the front face of the telephone support plate and is formed in front of each of the push-buttons with a relatively thick protruding tab portion. Thus, the membrane seals the apertures around the push-buttons while allowing the same to be depressed via the protruding tab portions of the membrane. Means such as the switches associated with the push-buttons urge the push-buttons and the overlying tab portions of the membrane forward from the front face.
The shield assembly of that invention further includes a rigid shield plate formed with an array of throughgoing apertures aligned with and generally identical to those of the support plate and having a rear face confronting the front face of the support plate and an opposite front face. The tab portions of the membrane project forward through the apertures of the shield plate past the front face thereof. The shield plate is itself secured in front of the membrane with the apertures aligned. Respective rigid caps fitted over the protruding tab portions project forward through the shield-plate apertures and each have an outwardly projecting flange extending generally parallel to and lying between the plates and of greater size than the respective shield-plate aperture. These flanges are urged forward against the rear face of the shield plate by the underlying protruding portions of the membrane, and in turn by the telephone push buttons.
In such an assembly the relatively delicate membrane is not exposed at all, while still effectively preventing any leakage around the push-buttons through the support plate, e.g. the telephone faceplate. Only the rigid caps and shield plate are exposed, and these elements can be quite rugged. The shield plate of this invention is typically made df steel, and the membrane is of an elastomeric material such is a silicone rubber. This combination of materials makes an extremely durable shield that seals very tightly.
In accordance with another feature of that invention the shield-plate apertures and caps are complementarily polygonal, normally square. The membrane is formed at each pushbutton with a respective protruding portion which has a height greater that that of the rigid cap which covers same and projects through the shield plate. This maintains the flange of the covers in good contact with the shield plate to provide a relatively close seal. Additionally the shield plate apertures are formed by being punched through from the underside of the plate, i.e. from the side which lies adjacent the membrane. This produces a shoulder or burr about the outwardly facing periphery of the apertures, making it difficult for a vandal to insert a pointed object into the space between the caps and the shield plate.
In addition, the height of the capped projections above the shield plate is designed to be less than the total available travel of the underlying telephone push-button which is moved by pressure on the capped projection. Accordingly, even when the distal end of the capped projection is flush with the outward face of the shield plate: the telephone push-button has not quite bottomed. This assures that a vandal will not damage the switching mechanism even by impacting the capped projections with a hammerlike object--notably the telephone receiver.
According to a further feature of that invention, the caps taper forward from the flanges and fit snugly within the respective shield-plate apertures when the respective flanges abut the rear face thereof. Thus the caps effectively seal the shield-plate apertures when in the fully out position.
The shield-plate of that invention has a backwardly turned outer peripheral rim. The membrane is recessed within this rim, making it virtually impossible to pry off the assembly according to the invention.
The keypad shield assembly further has means for securing the membrane and the shield plate to the front face of the support plate. This means can be a layer of adhesive on the back face of the membrane. It may also be constituted by a plurality of threaded studs projecting back from the back face of the shield-plate through the membrane and support plate.
The present invention utilizes some of the features described above and in my aforementioned U.S. Pat. No. 4,555,600, however, the present invention eliminates the need for the existing push-button, touch-tone, or pulse-tone switch arrangement in the telephone system and substitutes therefor a contact plate which acts as the electrical switch which responds to contact by the various push-buttons. The electrical contact switching plate has three soft layers mounted on a base layer which is a solid metallic surface. The first soft layer includes a first set of electrical leads and contact points. An intermediate spacing layer and a third top layer consisting of a second set of electrical leads and contact points overlie the first layer and the background. The leads are brought out for use via a ribbon cable formed integrally with the top layer.
As will be seen, the push-buttons now contact a surface of the top layer of the switch plate and cause the top layer to contact the bottom layer via the intermediate layer. An indication is developed when the contact is made amongst the layers of the switchplate.
The push-buttons of the invention described in the aforementioned U.S. Pat. No. 4,555,600 included a flexible membrane which overlaid the front face of the telephone support plate. The membrane contained protruding portions on which the push-buttons were mounted. Depressing a metallic cap mounted on that portion of the membrane caused the membrane to flex and thereby caused the corresponding underlying pushhutton of the telephone set to also depress. As taught in the U.S. Pat. No. 4,555,600, the "feel" and resilience of the push-buttons are, in part, developed by the pressure exerted by the buttons of the switch on the telephone set itself.
As the present invention eliminates the use of the telephone set push-buttons and substitutes therefore a mechanical switch matrix of a layered type, the push-buttons of the present invention still use a membrane mounted in a manner similar to that in the copending application. However, since the "feel" and/or resilience of the buttons can no longer utilize the forces exerted by the buttons of the telephone set, a modification to the membrane has been made to deliver the proper "feel" to the user of the push-button switch. Further, the membrane is designed such that the distance of travel of the push-button to contact the pressure actuated mechanical switch is limited to avoid damage to the switch as by permanent deformation therof. This resilience and control is achieved by having the protrusions of the membrane formed on a frustro-conical support base. This shape of base allows for an initial high resistance to the touch and then lower resistance to insure that good contact is made by the protrustion with the pressure-actuated switch.